High temperature tantalum-columbium base alloys



HIGH TEMPERATURE TANTALUM-COLUMBIUM Y BASE'ALLQYS Rudolf H. Thielernann, Pal o Alto,. Cali f., assignor to Sierra Metals Corporation, a eorporation of Delaware No Drawing. Applicationiluly 1,1957 Serial No. 668,892

Thisinvention relates to a tantalumcolumbiumchromium baseinetalalloy, and particularly to' one such alloy .Wllich contains chromium and tungsten, which alloy has engines, 'Other irnportant usestof the alloy of this invention are that it may beus'ed as exhaust valves and manifolds in internalcoinbuStidn engines, in heatexchangers, and as linings for retorts and containervessels used in the chemical and metallurgical industries. as e The prior art high tejmperature, high strength base metal alloys such as the nickel and/or cobalt base metal alloys which have been used :asblades, vanes and other parts of high temperature gas turbinedengines, have a maximum operating temperature of about 1500 F. For

example, a commdn nickel-cobalt base metalf'allo'y which incorporates molybdenum as a constituent is for all practical purposes non utilizable as a structural member in a gas turbine engine if the metal temperature significantly exceeds about 1500 F. because o f'the strength and oxidation resistancebl iinitations' of I such an alloy above this temperature.

In contrast, the: alloy of "this" invention when usedas a blade ,orvane ina hig'h temperature gas turbine engine cantheloperated at markedly higher temperatures than was possible heretofore, and the performance of the gas turbine engine is improved. in that thetotal thrust is in- An alloy of this invention isparticula rly resistantto oxidation and has high strength at elevated temperatures of about 2000" F. and higher, so as to: be suitable for use in forming liners for retorts and container vessels used creased and the amount of tuel consumedpe'r' pound of in the chemicaland metallurgical industries.

The'l inetal alloy this invention is comprised, by weight, of approximately percentto 20 percent of chromium, 2 percent to 25 percent of tungsten, and the balance, essentially a mixture of tantalum and jcolumbiurm the mount of tantelnin'in the mixture of tantalum and columbium being from about lOTperCent to "95 percent, and the balance of the mixture being essentially columbium. The proportions of the preferred alloys of this invention are, by weight, approximately percent United States Patent O 7 to 20 percent of chromium; 5 percent to 15 percent of tungsten, and the balance, essentially a mixture of tan- 2,907,654 Patented Oct. 6, 1959 2 t 1 columbium are substantially equivalent.. I have found thatthis is not the casein the present invention. Thus, forlexample, Lhavefound that a relatively small amount of chromium as an alloying constituent with .columbiurn and tungsten renders the resulting columbium-tungstenchromiumumetal alloy too brittle to be of any practical use. :On the other hand, I have discovered that when tantalum is alloyed with columbium and tungsten in the proportions specified above, then materially larger .proportions of chromium can be incorporated, resulting in the new tantalum-columbium-tungsten-chromium alloy of this iinve'ntionhaving unexpected, improved properties as indicated above. These properties are not achieved with ,a columbium-tungsten-chromium metal alloy.

To achieve the optimum desired properties in an allo .of the present invention, the impurities named below preferably should be held to the following approximate limits by weight. The carbon content in thefinal alloy preferably should be no more than 0.5 percent; the oxygen content, no more than 0.8 percent, as determined by .an increase on ignition technique; the nitrogen content,

Eramplel An ingot of a tantalumcolumbium-chromium-tungsten metal alloy composition containing by Weight 15, percent offchromium, 15 percent oftungsten, 3.5 percent of columbiu nancl the balance, essentially tantalum, was

prepared *by are melting an electrode of tantalum to which35 percent columbium, 1-5 percent tungsten and 15 percent chromium were added. This may be accomplished by pressing a uniform powder mix of tantalum, 'columbium, chromium and tungsten in the above proportions in the formof bars under a pressure of about 50 tons per square inch, sintering the pressed bars under a vacuum condition of about 1 micron for a period of about 3 hours, and then are melting the sintered bars under a vacuumcondition of about 5 microns or less.

The are melted alloy of this example was tested for oxidation resistance in inoving air at about 2000 F. for twent'y four hours. Its resistance to oxidation was about 700 times greater than the resistance to oxidation of substantially pure columbium. i i

The test procedure for oxidation resistance was comprised of preparing test samples of the alloy and the dimensions of such test samples determined prior to subjecting the test samples to the oxidation test conditions. The oxide film which formed on the test samples during testingwas removed and the thickness of each tested sample was then measured and compared with the thickness of the test sample prior to submitting it to the test conditions. The same procedure was carried out to determine the oxidation resistance of substantially pure eolumbium and a comparison made between the oxidation resistance of colnm biu m and the alloy of this e am e i f flest bar s (4A ineh diameter and 3 inches long) were fabricated frem the are melted ingot of this example by hot-working procedure. The hour a rupture strength of; such bars in moving air at about 2000". F. exceeded 20,000 pounds per square inch (p.s.i.). a

Example. 2

An ingot of a tantalum-chromium-columbiurirtungsten metal alloy composition containing by weight 10 percent of chromium, 10 percent of tungsten, 24 percent of tantalum, and the balance, essentially columbium,

' in Example 1.

' in Example 1.

was prepared in the same manner as set forth in 'Example 1.

The are melted alloy of this example was tested for.

Example 3 An ingot of a tanalum-columbium-chromium-tungsten metal alloy composition containing by weight percent of chromium, 25 percent of tungsten, 7.3 percent of tantalum and the balance, essentially columbium, was prepared in the same manner as set forth in Example 1.

The are melted alloy of this example was tested for oxidation resistance in moving air at about 2000 F. for twenty-four hours in the same manner as set forth The resistance to oxidation of the example of this alloy is about 100 times greater than the oxidation resistance of substantially pure columbium.

Test bars A inch diameter and 3 inches long) were fabricated from the arc melted ingot of this example by hot-working procedure. Test bars of this example 1 had a 100 hour rupture strength in excess of 20,000 p.s.i.

in moving air at about 2000 F.

7 Example 4 An ingot of a tantalum-columbium-chromium-tungsten metal alloy composition containing by weight 20 percent of chromium, 5 percent of tungsten, 7.5 percent of columbium and the balance, essentially tantalum,

was prepared in the same manner as set forth in Example 1. a

The are melted alloy of this example was tested for oxidation resistance in moving air at about 2000 F.

for twenty-four hours in the same manner as set forth melted alloy of this example is about 800 times greater than the oxidation resistance of substantially pure columbium.

Test bars inch diameter and 3 inches long) were fabricated from the are melted ingot of this example by hot-working procedure. The test bars of this example had a 100 hour rupture strength in excess of 20,000 p.s.i. at a temperature of about 2000 F. in moving air. I

* Example 5 An ingot of a tantalum-columbium-chromium-tungsten metal alloy composition containing by weigh t percent of chromium, 10 percent of tungsten, 40 percent of columbium, and the balance, essentially tantalum, was prepared in the same manner as set forthin Example 1,

The arc meltedalloy of this example was tested for oxidation resistance in moving air at about 2000" F. for twenty-four hours in the same. manner described in Example 1. The oxidation resistance of the-alloy of this example is aboutv 500 times greater than the oxidation resistance of substantially pure columbium.

Test bars A'inch diameter and 3 inches'long) were fabricated from the arc melted ingot of this example by hot-working procedure. The test bars of this example had a 100 hour rupture strength in excess of 20,000 p.s.i. at a temperature of about 2000 F. in moving air. a r r The test bars had a 100 hour The oxidation resistance of the arc 4, Example 6 An ingot of a tantalum-columbium-chromium-tungsten metal alloy composition containing by weight 5 percent of, chromium, 2 percent of tungsten, 18.6 percent of tantalum, and the balance, essentially columbium, was prepared in the same manner as set forth in Example 1. 1

The are melted alloy of this example was tested for oxidation resistance in moving air at about 2000 F. for twenty-four hours in the same manner as described in Example 1. The oxidation resistance of the arc melted alloy of this example was about 100 times greater than the oxidation resistance of substantially pure columbium.

Test bars A inch diameter and 3 inches long) were fabricated from the arc melted ingot by hot-working procedure. The test bars of this example had a 100 hour rupture strength in excess of 20,000 p.s.i. at a temperature of about 2000 F. inmoving air.

I claim:

1. A metal alloy which comprises, by weight: 5 percent to 20 percent chromium; ,2 percent to 25 percent tungsten; and the balance, essentially a mixture of tantalum andcolumbium, the amount of tantalum in the mixture of tantalum and columbium being from 10 percent to percent of the mixture, the balance of the mixture being essentially columbium.

2. A metal alloy which comprises, by weight: 10 percent, to 20 percent chromium; 5 percent to. 15 percent tungsten; and the balance, essentially a mixture of tantalum and columbium, the amount of tantalum in the mixture of tantalumand columbium being from '30 percent to 95 percent of the mixture, the balance of the mixture being essentially columbium.

3. A metal alloy which comprises, by weight: 10 percent chromium; 10 percent tungsten; and the balance, essentially a mixture of tantalum and columbium, the amount ,of tantalum in the mixture of tantalum and columbium being about 24 percent'of the mixture and the balance of the mixture being essentially columbium.

4. A metal alloy which comprises, by weight: 10 percent chromium; 10 percent tungsten; and the balance, essentially a mixture of tantalum and columbium, the amount of columbium in the mixture of tantalum and columbium being about 40 percent of the mixture and the balance of the mixture being essentially tantalum.

5. A metal alloy which comprises, by weight: 5 percent to 20 percent chromium; 2 percent to 25 percent tungsten; and the balance, essentially a mixture of tantalum and columbium, the amount of tantalum in the mixture of tantalum and columbium being from 10 percent to 95 percent of the mixture, the balance of the mixture being essentially columbium, the impurities carbon, oxygen, nitrogen, and iron not exceeding 0.5 percent of carbon, 0.8 percent of oxygen, 0.2 percent of nitrogen, and 5 percent of iron.

6. A metal alloy which comprises, by weight: 10 percent ot 20 percent chromium; 5 percent to 15 percent tungsten; and the balance, essentially a mixture of tantalum and columbium, the amount of tantalum in the mixture of tantalum and columbium being from 30 percent to 95 percent of the mixture, the balance of the mixture being essentially columbium, the impurities carbon, oxygen, nitrogen, and iron notexceeding 0.5 percent of carbon, 0.8 percent of oxygen, 0.2 percent of nitrogen,

and 5 percent of iron.

References Cited in the tile of this patent UNITED STATES PATENTS 

1. A METAL ALLOY WHICH COMPRISES, BY WEIGHT 5 PERCENT TO 20 PERCENT CHROMIUM; 2 PERCENT TO 25 PERCENT TUNGSTEN, AND THE BALANCE, ESSENTIALLY A MIXTURE OF TANTALUM AND COLUMBIUM, ATHE AMOUNT OIF TANATALUM IN THE MIXATURE OF TANTALUM AND COLUMBIUM BEING FROM 10 PERCENT TO 95 PERCENT OF THE MIXTURE, THE BALANCE OF THE MIXTURE BEING ESSENTIALLY COLUMBIUM. 